(a) Field of the Invention
The present invention relates to a hydraulic control system for an automatic transmission, and more particularly, to a hydraulic control system applied to a powertrain utilizing two single pinion planetary gearsets, four clutches, two one-way clutches, and two brakes to obtain four forward speeds and one reverse speed.
(b) Description of the Related Art
Conventional automatic transmissions used in vehicles include a torque converter, a multi-stage gear shift mechanism connected to the torque converter, and a plurality of friction elements actuated by hydraulic pressure for selecting one of the gear stages of the gear shift mechanism, the gear shift mechanism being realized through a planetary gearset. The friction elements are controlled to engaged and disengaged states by a hydraulic control system, which controls pressure generated by an oil pump, to change shift ratios of the planetary gearset.
The friction elements are selectively operated by a plurality of valves, which undergo port conversion to change the flow of hydraulic pressure, and actuators supplying hydraulic pressure to the valves. Further, a manual valve, indexed with a driver-operated shift selector to realize port conversion, is connected to a plurality of lines to supply hydraulic pressure from the oil pump to each valve and actuator.
Solenoid valves are operated to ON and OFF states in different combinations to realize control into the various speeds and shift modes. That is, as described above, the solenoid valves are operated to ON and OFF states such that the supply of hydraulic pressure to the valves is controlled. This, in turn, controls the supply of hydraulic pressure to specific friction elements to control the same, thereby ultimately controlling the multi-stage gear shift mechanism for control into the different shift speeds and modes.
However, in the prior art hydraulic control system, an engine brake is applied frequently at unsuitable times such that drive performance is reduced. Also, fail-safe means in case the transmission malfunctions is not provided.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a hydraulic control system applied to a powertrain utilizing two single pinion planetary gearsets, four clutches, two one-way clutches, and two brakes to obtain four forward speeds and one reverse speed, the hydraulic control system operating an engine brake at only a high stage of each range such that drive performance is improved and which provides a fail-safe mode by holding a fourth speed in a drive D range and a third speed in a low D2 range such that drive performance is improved.
To achieve the above object, the present invention provides a hydraulic control system in which hydraulic pressure generated by the operation of an oil pump is supplied to pressure/damper clutch control means, pressure reducing means, and shift control means, pressure reduced by the pressure reducing means and hydraulic pressure supplied as a result of port conversion of the shift control means being supplied to hydraulic pressure control means, and hydraulic pressure controlled by the hydraulic pressure control means being supplied to hydraulic pressure distribution means and directly to selective friction elements to engage the same.
The shift control means includes a manual valve which is indexed with a driver-controlled select lever to supply hydraulic pressure through five different lines to the hydraulic pressure control means, the hydraulic pressure distribution means, and the friction elements,
The hydraulic pressure control means includes first, second and third pressure control valves which are controlled by pressure controlled by first, second and third solenoid valves, the first pressure control valve controlling hydraulic pressure to be directly supplied to a first clutch operating in forward shift modes, the second pressure control valve controlling hydraulic pressure to be supplied to a second brake operating in second and fourth speeds of a drive D range, and the third pressure control valve controlling hydraulic pressure to be supplied to a first brake operating in a low L range and a reverse R range and to a third clutch operating in third and fourth speeds of the drive D range such that hydraulic pressure is supplied to two valves of the hydraulic pressure distribution means.
The hydraulic pressure distribution means comprises a low control valve for supplying L-range pressure to another valve as control pressure in the low L range such that control pressure of the third pressure control valve is supplied to the first brake; an N-R control valve for supplying reverse pressure to the first brake by reduced pressure supplied via the pressure control valve when shifting into the reverse R range; a line pressure control switch valve controlled by D-range pressure and hydraulic pressure supplied to a second clutch, the line pressure control switch valve supplying a part of the hydraulic pressure supplied to the second clutch to a pressure regulator valve; a first failsafe valve controlled by control pressure supplied from the low control valve and from the second pressure control valve, the first fail-safe valve undergoing port conversion to supply hydraulic pressure supplied from the third pressure control valve to the second clutch in the third and fourth speeds of the drive D range, and hydraulic pressure supplied from the third pressure control valve to the first brake in the low L range; a second fail-safe valve controlled by reverse pressure, hydraulic pressure supplied to a fourth clutch, and hydraulic pressure supplied to the third clutch, the second fail-safe valve supplying hydraulic pressure supplied from the second pressure control valve to the second brake in the second and fourth speeds of the drive D range; and an engine brake control switch valve for supplying D-range pressure to the fourth clutch in the first and third speeds of the drive D range.
According to a feature of the present invention, the manual valve is connected to a reverse R range pressure line directly communicated with the third clutch; a forward pressure line connected to the pressure regulator valve; a drive D range pressure line connected to the first, second and third pressure control valves, the second fail-safe valve, and the engine brake control switch valve; a low D2 range pressure line connected to the fourth clutch with a 3-way valve interposed therebetween; and a low L range pressure line connected to the low control valve.
According to another feature of the present invention, the first, second and third solenoid valves are 3-way valves which maintain a closed state when controlled to OFF.
According to yet another feature of the present invention, a valve body of the first pressure control valve includes a first port for receiving hydraulic pressure reduced by a reducing valve; a second port for receiving hydraulic pressure from the manual valve; a third port for supplying the hydraulic pressure received by the second port to the first clutch; and a fourth port for receiving control pressure from the first solenoid valve;
a valve spool of the first pressure control valve slidably provided in the valve body of the first pressure control valve includes a first land on which the hydraulic pressure supplied through the first port acts, the first land having a relatively small diameter; a second land on which the hydraulic pressure supplied through the first port acts to selectively open and close the second port; and a third land which, together with the second land, selectively communicates the second port and the third port; and
an elastic member is disposed between the third land and the valve body.
According to still yet another feature of the present invention, a valve body of the second pressure control valve includes a first port for receiving hydraulic pressure reduced by a reducing valve; a second port for receiving hydraulic pressure from the manual valve; a third port for supplying the hydraulic pressure supplied to the second port to the first fail-safe valve and the engine brake control switch valve; a fourth port for receiving control pressure from the second solenoid valve; and a fifth port for supplying as control pressure the control pressure supplied to the fourth port;
a valve spool of the second pressure control valve slidably provided in the valve body of the second pressure control valve includes a first land on which the hydraulic pressure supplied through the first port acts, the first land having a relatively small diameter; a second land on which the hydraulic pressure supplied through the first port acts to selectively open and close the second port; and a third land which, together with the second land, selectively communicates the second port and the third port; and
an elastic member is disposed between the third land and the valve body.
According to still yet another feature of the present invention, a valve body of the third pressure control valve includes a first port for receiving hydraulic pressure reduced by a reducing valve; a second port for receiving hydraulic pressure from the manual valve; a third port for supplying the hydraulic pressure supplied to the second port to the first and second fail-safe valves; and a fourth port for receiving control pressure from the third solenoid valve;
a valve spool of the third pressure control valve slidably provided in the valve body of the third pressure control valve includes a first land on which the hydraulic pressure supplied through the first port acts, the first land having a relatively small diameter; a second land on which the hydraulic pressure supplied through the first port acts to selectively open and close the second port; and a third land which, together with the second land, selectively communicates the second port and the third port; and
an elastic member is disposed between the third land and the valve body.
According to still yet another feature of the present invention, a valve body of the low control valve includes a first port receiving low L range pressure; a second port for supplying to the first fail-safe valve the hydraulic pressure supplied to the first port; a third port for receiving from the first fail-safe valve the hydraulic pressure supplied to the second clutch; and a fourth port for receiving as control pressure a part of the hydraulic pressure supplied to the first brake;
a valve spool of the low control valve slidably provided in the valve body of the low control valve includes a first land on which the control pressure supplied to the third port acts to selectively open and close the first port; and a second land for selectively communicating the second port with an exhaust port; and
an elastic member is disposed between the second land and the valve body.
According to still yet another feature of the present invention, a valve body of the N-R control valve includes a first port communicated with the second pressure control valve; a second port communicated with a reverse R range pressure line; and a third port for selectively supplying the hydraulic pressure supplied to the second port to the first brake via the first fail-safe valve;
a valve spool of the N-R control valve slidably provided in the valve body of the N-R control valve includes a first land on which the hydraulic pressure supplied to the first port acts; and a second land for opening and closing the second and third ports; and
an elastic member is disposed between the second land and the valve body.
According to still yet another feature of the present invention, a valve body of the line pressure control switch valve includes a first port for receiving drive D range pressure; a second port for receiving second clutch pressure; and a third port for supplying the hydraulic pressure supplied to the second port as variable line pressure to the pressure regulator valve; and
a valve spool of the line pressure control switch valve slidably provided in the valve body of the line pressure control switch valve includes a first land on which the hydraulic pressure supplied to the first port acts; and a second land for selectively communicating the second and third ports.
According to still yet another feature of the present invention, a surface area of the second land on which hydraulic pressure acts is larger than a surface area of the first land on which hydraulic pressure acts.
According to still yet another feature of the present invention, a valve body of the first fail-safe valve includes a first port for receiving control pressure from the low control valve; a second port for receiving hydraulic pressure from the third pressure control valve; a third port for receiving hydraulic pressure from the N-R control valve; a fourth port for selectively supplying the hydraulic pressure supplied to the second port to the second clutch; fifth and sixth ports for supplying the hydraulic pressure supplied to the third port to the first brake and the low control valve; and a seventh port for receiving control pressure from the second pressure control valve;
a valve spool of the first fail-safe valve slidably provided in the valve body of the first fail-safe valve includes a first land on which the control pressure received through the first port acts; a second land selectively communicating the second port and the fourth port, and, together with the first land, communicating the third port with the fifth and sixth ports; and a third land on which the control pressure received through the seventh port acts; and
an elastic member is disposed between the third land and the valve body.
According to still yet another feature of the present invention, a valve body of the second fail-safe valve includes first, second, third and fourth ports connected respectively to a reverse R range pressure line, the fourth clutch, the third pressure control valve and a drive D range pressure line; a fifth port for receiving hydraulic pressure from the second pressure control valve; and a sixth port for supplying the hydraulic pressure supplied to the fifth port to the second brake;
a valve spool of the second fail-safe valve slidably provided in the valve body of the second fail-safe valve includes first, second and third lands on which the hydraulic pressure supplied respectively through the first, second and third ports acts; a fourth land selectively communicating the sixth port with an exhaust port and the fifth port; a fifth land selectively communicating the fifth port with the sixth port; and a sixth land on which control pressure received through the fourth port acts, the sixth land being surrounded by a sleeve of the valve body.
According to still yet another feature of the present invention, a valve body of the engine brake control switch valve includes a first port for receiving control pressure from the second pressure control valve; a second port connected to a low D2 range pressure line, the low D2 range pressure line being connected to the manual valve; and a third port for supplying the hydraulic pressure supplied to the second port to the fourth clutch;
a valve spool of the engine brake control switch valve slidably provided in the valve body of the engine brake control switch valve includes a first land on which the hydraulic pressure supplied through the first port acts; and a second land selectively communicating the second port and the third port; and
an elastic member is disposed between the second land and the valve body.
According to still yet another feature of the present invention, the fourth clutch receives D-range pressure either via the engine brake control switch valve or directly from a low D2 range pressure line.
According to still yet another feature of the present invention, the engine brake control switch valve and the low D2 range pressure line are connected to the fourth clutch with a 3-way valve interposed therebetween.